1. Field of the Invention
The present invention relates to a speech output control device for use in electronic apparatuses having a speech output function and driven by a battery, and a recording medium recorded with speech output control programs.
2. Description of the Related Art
Conventionally, electronic apparatuses having a speech output function, such as audio equipment, include an output volume control device that optimizes the volume and tone of output speech in accordance with various use environments of the electronic apparatuses.
For example, vehicle-mounted audio equipment includes an output volume control device. The output volume control device varies the volume and tone of output speech in accordance with its surrounding noise level. When the noise level rises to distort the output speech, the output volume control device controls the volume such that an audience can easily listen to the output speech.
The speech output device of a personal computer includes an output volume control device. The output volume control device controls the output volume and sets it at a fixed level each time the speech output device receives speech signals of different recording levels. When the device outputs a different speech signal at the same volume level as that of the last speech signal, it controls the volume of the output speech signal and prevents it from being distorted.
The above prior art output volume control devices compress an input speech signal over a dynamic range in order to prevent an output speech from being distorted in consideration of an external influence such as a surrounding noise level and an output gain of volume.
There is a small-sized electronic device, such as an electronic dictionary with a speech output function, which outputs reading speech of text such as words and examples. The dynamic range of the output reading speech is greatly widened in accordance with the rhythm, stress, and intonation of reading.
Such a small-sized electronic device is driven by a battery. It is thus necessary to control the volume of text speech and restrict its maximum output volume in order to prevent the maximum part of text speech from being powered down due to a temporary voltage drop even though the battery is almost dead. If, however, the maximum output volume is restricted, a user can hardly listen to or cannot listen to a low-level part of the text speech.
When text speech data of recorded real speech is output, a low-level part of the recorded speech can be raised to an audible level in advance. However, when not recorded speech but reading text speech is synthesized and the synthesized speech is output in real time, the volume level cannot be controlled (changed) in advance.